1. Field of the Invention
The present invention relates generally to scanning documents. More specifically, systems and methods using an orientation and/or position sensitive calibration pattern for three-dimensional calibration of an imaging system, such as may be used in a process for scanning documents, particularly bound documents, are disclosed.
2. Description of Related Art
Scanning books, magazines, and other printed material into digital form has become more common with the advent of improved imaging, storage and distribution techniques. Although unbound printed material can generally be scanned with relative ease using automatic page-feeding mechanisms such as those commonly found on digital copiers and scanners, bound documents present additional challenges. Bound documents include not only books, but also periodicals, manuscripts, pamphlets, brochures, newspapers, manuals, and any other document having a bound edge. Many institutions, such as the libraries, universities, bookstores, and private enterprises have vast collections of bound documents. By converting these documents into electronic form, such institutions can reduce the cost of storage, facilitate remote access, enable simultaneous access by multiple users, facilitate search and retrieval of information, and/or protect information in rare or out-of-print works from loss or destruction.
Once the content of a bound document is scanned, the recorded image can be manipulated or otherwise processed. Digitally recorded bound documents can be de-warped, reformatted, supplemented with additional information, compressed, and/or processed with OCR (optical character recognition) software, and indexed to facilitate electronic search. Thus, scanning and recording of bound documents facilitates the creation of digital libraries that can be remotely and simultaneously accessed and searched by multiple users.
Various mechanisms have been developed to enable the scanning of bound documents. For example, a traditional flat-bed platen scanner scans bound documents in a face-down position. However, for best results, a flat-bed scanner typically requires the application of force to the spine or binding region of the bound documents to insure that they come within the scanner's depth of focus. Such force can damage the spine region of the document. In addition, using the flat-bed platen can be tedious and time-consuming, as the bound documents typically must be lifted and repositioned after each page is scanned. Further, image quality is often poor due to loss of focus, uneven illumination, and/or distortion caused by page curvature in the vicinity of the binding.
An alternative to the traditional flat-bed platen scanner is a platen-less scanner that captures image data from a bound document in a face-up position. Such scanners typically do not require application of additional stress to the binding region of a bound document, since the document is scanned in its natural, face-up position. Some such scanners may make use of automatic page turning apparatuses.
In such platen-less scanning systems, three-dimensional calibration of the imaging system may be performed to determine, for example, the exact position and orientation of the cameras, zoom factors, distortion of the lenses, etc. Conventional calibration schemes generally require the calibration pattern to be completely visible within the images of the cameras to be calibrated. Such a requirement may be extremely difficult to satisfy in a system where the cameras' fields of view may not overlap by a significant amount. Where the fields of view of the cameras do not overlap significantly, there is only a very limited area where the entire calibration pattern would be visible by all cameras. Thus, it would be desirable to provide systems and methods for improved three dimensional calibration of image capturing systems.